Tell me how to pack liquid in a folding board cartion?
It depends on what type of liquid you are packing as well as its destination and purpose.
I will assume that you are not sending this package through the mail or by any commercial carrier. If you are, follow their instructions for proper packaging, particularly if the liquid is in any way toxic or corrosive.
In general, the process is simple. Put the liquid in a tightly sealed container. Plastic is best if the liquid is non-corrosive. Use bubble wrap as the first layer of protection. You can cover the container with the bubble wrap and secure it with tape. You may also choose to use bubble wrap inside the box or substitute it with packing peanuts, shredded paper or some similar material. Ensure that the container is placed securely in the box. Tape the box closed and everything should be fine.
You may also choose to mark the box so that any handler will take care.